Theoretical Temperature–Pressure Phase Diagram for {N(CH₃)₄}₂ZnI₄

Abstract

Theoretical phase diagrams for {N(CH 3 ) 4 } 4 ZnI 4 crystal are constructed using the phenomenological approach, which was developed earlier for {N(CH 3 ) 4 } 4 M Cl 4 family crystals. On these diagrams, as well as on the experimental diagram, there are three commensurate phases and there is no incommensurate phase. To explain this the phase transition from the initial phase to the phase with q =1/2 is considered to be first order. The theoretical temperature–pressure phase diagram is plotted and is found to be in agreement with the experimental diagram. The approximations and assumptions made in the construction of theoretical diagrams are discussed.